1. Field of the Invention
The present invention relates generally to fasteners and, more particularly, to a new expansion fastener for anchoring an unthreaded rod in a hole provided on the face of an existing rock or concrete structure.
2. Description of the Prior Art
Fasteners that connect an external member to an existing structure are sometimes called "blind fasteners" because they are "blindly" installed on the face of the existing structure without being accessible from the other side. The present invention is directed towards a type of blind fastener that is typically used to construct a concrete form adjacent to an existing structure or to place reinforcement bar ("re-bar") in an existing structure.
Concrete forms usually include form ties that extend between the walls of the form. The form ties prevent the walls of the concrete form from spreading under the outward forces present during the placement of wet concrete. When constructing an ordinary "free-standing" concrete form that includes two spaced form walls, it is relatively easy to install the form ties because they extend through and are accessible on either side of the concrete form.
It is much more difficult to construct a concrete form adjacent to an existing concrete, masonry, rock, or other structure. In this circumstance, the concrete form consists of the existing structure and a single adjacent form wall. The form ties must somehow be "blindly" connected to and extend from the existing structure. Hence, the need for a simple, cost effective, and easily installed blind fastener.
Blind fasteners are also used for the placement of concrete reinforcement in an existing structure. In this instance, the blind fastener is placed in an existing structure in order to support deformed concrete reinforcement bar ("re-bar").
FIGS. 7 through 9 depict several known fasteners. One prior art blind fastener is called a drop-in anchor (see FIG. 6). A drop-in anchor is comprised of an expansion sleeve 51 that has an aperture 52 with internal threads 53 on one end. The diameter of the aperture 51 is constant for the length of the threads but then tapers gradually towards the other end from where the threads 53 stop. A conical plug 54 is located in the threaded aperture 52 at the start of the taper. A drop-in anchor 50 is installed by first drilling a proper sized hole 56 in the existing structure, by "dropping" the expansion sleeve 51 in the hole 56, and by then expanding the sleeve 51 by driving the conical plug 54 further into the tapering portion of the aperture 52 with an appropriate tool. The installation is completed by turning a threaded rod 57 into the threads 53 of the sleeve.
FIG. 7 shows a different kind of drop-in anchor 60 where a conical plug 64 extends into a rear portion 68 of the sleeve 61. The anchor 60 is installed by dropping the sleeve 61 and the conical plug 64 into a hole 66 drilled in the existing structure and by then punching the sleeve 61 down onto the conical plug 64. The sleeve 61 expands when the plug is driven 64 into the sleeve 61. As before, a threaded rod 67 must then be threaded into the sleeve 61.
An improvement over the drop-in anchors 50, 60 is provided by a type of blind fastener referred to here as a "cone/sleeve" anchor 70 (see FIG. 8). Cone/sleeve anchors, like drop-in anchors, must also use continuous coil rods or rods with threaded ends. The cone/sleeve anchor 70 is comprised of a threaded cone 74, an expansion sleeve 71, and a thrust ring 79. The cone/sleeve anchor is installed by first locking the thrust ring 79 onto the threaded rod 77 (method not shown). Next, the expansion sleeve 71 is slipped onto the rod 77 until it rests against the thrust ring 79 and is prevented from sliding further up the rod. Finally, the threaded cone 74 is turned onto the threaded end 78 of the rod and so that its narrow end wedges into the expansion sleeve 71. The entire assembly is then inserted into a hole 76 drilled in the existing structure and the threaded rod 77 is turned so that the cone 74 is tightened into the expansion sleeve 71 which then expands and seats in the hole 76.
The cone/sleeve anchor 70 is desirable over either of the drop-in anchors 50, 60 because pulling forces from the rod tend to reinforce the connection by pulling the cone 74 further into the sleeve 71. However, as with the drop-in anchors 50, 60, the cone/sleeve anchor 70 requires a threaded rod, making it time consuming to install and difficult to extract after placement of the concrete.
Another prior art fastener is sold under the trade name "Rock Anchor" 80 (see FIG. 9). The Rock Anchor includes an expansion shell 81 that is comprised of two cylindrical halves 81a, 81b that are held adjacent to one another with a U-shaped "back stop" member 87. The adjacent edges of the two cylindrical halves 81a, 81b are angled to define a wedge-shaped gap 82 that opens towards the back stop 87. A wedge member 84 is loosely supported by the back stop 87 and oriented so that the narrow side of the wedge member 84 is directed into the wedge-shaped gap 82 between the two cylindrical halves 81a, 81b. The wedge member 84 contains a threaded aperture 84a for engagement with a threaded rod 87 inserted through the expansion shell 81. The Rock Anchor 80 is placed in a hole 86 and when the threaded rod 87 is tightened, the wedge member 84 is pulled into the gap 82, the two halves 81a, 81b expands, and the expansion shell 81 seats in the hole.
From the above description of the prior art, it can be seen that there is considerable room for improvement in the area of blind fasteners. In particular, the drop-in anchors 50, 60 are undesirable because the pulling forces transferred to the respective sleeve 51, 61 from the threaded rod tend to loosen the anchor rather than further secure it. Because of this tendency to loosen under stress, the safe working load (SWL) of the prior art fasteners is generally low, mandating a larger than desirable number of anchors for a given application. All of the prior art fasteners require a threaded rod, making it difficult and time consuming to install and remove the rod. Finally, threaded rods are generally metallic to provide the shear strength needed at the threads and are therefore relatively expensive and subject to rust or corrosion that may damage the appearance or structural integrity of the resulting structure.